1. Field of the Invention
The invention relates to a wheel bearing device.
2. Description of the Related Art
A wheel bearing device for fitting a tire wheel and a brake disc is used in a vehicle such as an automobile. The wheel bearing device includes an inner ring, an outer ring, rolling elements, and a sealing device (refer to, for example, Japanese Patent Application Publication No. 2008-45673 (JP 2008-45673 A)). The inner ring has a flange. The outer ring is disposed radially outward of the inner ring and is fixed to a vehicle body-side member. The rolling elements are disposed between the inner ring and the outer ring. The sealing device prevents foreign matter from entering the inside of a bearing where the rolling elements are disposed. The sealing device has a lip portion. The lip portion is in sliding contact with a part (seal face) of a side face of the flange. The wheel bearing device is used in an environment where foreign matter may adhere to the wheel bearing device. Examples of the foreign matter include rainwater and muddy water containing a snow melting agent used in a cold region. Thus, the sealing device is required to have high reliability and durability so that no rust is formed on, for example, raceway surfaces in the bearing.
In the sealing device described in JP 2008-45673 A, a clearance is formed between an end portion of the outer ring and the flange of the inner ring. Water (rainwater or muddy water) may be retained and stagnate in the clearance due to surface tension. The stagnation of the water in the clearance is likely to occur at a bottom portion of the wheel bearing device in a state where the vehicle is stopped and rotation of the inner ring is stopped. When the water stagnates as described above, rust is formed on the flange and the rust ultimately spreads to the seal face. In this case, when the inner ring rotates with the wheel, the lip portion that is in sliding contact with the seal face becomes significantly worn and the sealing function of the lip portion is reduced to cause water leakage. As a result, the water reaches the raceway surfaces on which the rolling elements (e.g., rollers and balls) roll and rust is formed on the raceway surfaces, and thus noise and vibration occur as the inner ring rotates.
Thus, there is a sealing device (deflector seal) 90 including a second lip portion 92 in addition to a first lip portion 91 that is in sliding contact with a part (seal face 93) of a flange 95 as illustrated in FIG. 4. The second lip portion 92 forms a small clearance d in cooperation with the flange 95 to constitute a labyrinth seal, thereby suppressing entry of the water.
As illustrated in FIG. 4, an inflection portion (edge) 96 is formed between the inner seal face 93 with which the first lip portion 91 is in sliding contact and an outer seal face 94 that forms the clearance d in cooperation with the second lip portion 92. The inflection portion 96 is close to a portion 97 of the sealing device 90. In addition, the region in which the portion 97 of the sealing device 90 and a part of the inner seal face 93 face each other in parallel is long. In this case, if even a small amount of water enters the inside of a bearing from the second lip portion 92, the water that has entered the inside of the bearing is retained and stagnates, due to the surface tension, between the portion 97 of the sealing device 90 and the inflection portion 96, and rust is likely to be formed on the inflection portion 96 and a region in the vicinity of the inflection portion 96.
The region where rust is formed is close to the inner seal face 93. Thus, as in the case of JP 2008-45673 A, the rust ultimately spreads to the inner seal face 93, and the first lip portion 91 that is in sliding contact with the seal face 93 is significantly worn as the inner ring rotates. Then, the function of the lip portion 91 is reduced and thus water leakage occurs. As a result, the water reaches the raceway surfaces of the wheel bearing device, on which rolling elements (e.g., rollers and balls) roll, and the rust is formed on the raceway surfaces. Consequently, noise and vibration occurs as the inner ring rotates, which may reduce the service life of the wheel bearing device.